Question

1783. Grand Slam Titles

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Description

Table: Players

+----------------+---------+
| Column Name  | Type  |
+----------------+---------+
| player_id    | int   |
| player_name  | varchar |
+----------------+---------+
player_id is the primary key (column with unique values) for this table.
Each row in this table contains the name and the ID of a tennis player.

 

Table: Championships

+---------------+---------+
| Column Name   | Type  |
+---------------+---------+
| year      | int   |
| Wimbledon   | int   |
| Fr_open     | int   |
| US_open     | int   |
| Au_open     | int   |
+---------------+---------+
year is the primary key (column with unique values) for this table.
Each row of this table contains the IDs of the players who won one each tennis tournament of the grand slam.

 

Write a solution to report the number of grand slam tournaments won by each player. Do not include the players who did not win any tournament.

Return the result table in any order.

The result format is in the following example.

 

Example 1:

Input: 
Players table:
+-----------+-------------+
| player_id | player_name |
+-----------+-------------+
| 1     | Nadal     |
| 2     | Federer   |
| 3     | Novak     |
+-----------+-------------+
Championships table:
+------+-----------+---------+---------+---------+
| year | Wimbledon | Fr_open | US_open | Au_open |
+------+-----------+---------+---------+---------+
| 2018 | 1     | 1     | 1     | 1     |
| 2019 | 1     | 1     | 2     | 2     |
| 2020 | 2     | 1     | 2     | 2     |
+------+-----------+---------+---------+---------+
Output: 
+-----------+-------------+-------------------+
| player_id | player_name | grand_slams_count |
+-----------+-------------+-------------------+
| 2     | Federer   | 5         |
| 1     | Nadal     | 7         |
+-----------+-------------+-------------------+
Explanation: 
Player 1 (Nadal) won 7 titles: Wimbledon (2018, 2019), Fr_open (2018, 2019, 2020), US_open (2018), and Au_open (2018).
Player 2 (Federer) won 5 titles: Wimbledon (2020), US_open (2019, 2020), and Au_open (2019, 2020).
Player 3 (Novak) did not win anything, we did not include them in the result table.

Solutions

Solution 1: Union All + Equi-Join + Group By

We can use UNION ALL to merge all player IDs who won Grand Slam titles into a table T, then use an equi-join JOIN to join T table with Players table on player_id, and finally use GROUP BY and COUNT to count the number of Grand Slam titles won by each player.

# Write your MySQL query statement below
WITH
  T AS (
    SELECT Wimbledon AS player_id
    FROM Championships
    UNION ALL
    SELECT Fr_open AS player_id
    FROM Championships
    UNION ALL
    SELECT US_open AS player_id
    FROM Championships
    UNION ALL
    SELECT Au_open AS player_id
    FROM Championships
  )
SELECT player_id, player_name, COUNT(1) AS grand_slams_count
FROM
  T
  JOIN Players USING (player_id)
GROUP BY 1;

Solution 2

# Write your MySQL query statement below
SELECT
  player_id,
  player_name,
  SUM(
    (
      CASE
        WHEN Wimbledon = player_id THEN 1
        ELSE 0
      END
    ) + (
      CASE
        WHEN Fr_open = player_id THEN 1
        ELSE 0
      END
    ) + (
      CASE
        WHEN US_open = player_id THEN 1
        ELSE 0
      END
    ) + (
      CASE
        WHEN Au_open = player_id THEN 1
        ELSE 0
      END
    )
  ) AS grand_slams_count
FROM
  Championships
  CROSS JOIN Players
GROUP BY player_id
HAVING grand_slams_count > 0;